Polishing agent, polishing method, and liquid additive for polishing

ABSTRACT

The present invention relates to a polishing agent including: a water-soluble polymer including a copolymer of a monomer (A) which includes at least one member selected from the group consisting of an unsaturated dicarboxylic acid, a derivative thereof, and salts of the unsaturated dicarboxylic acid and the derivative thereof and a monomer (B) other than the monomer (A), comprising an ethylenic double bond and no acidic group; a cerium oxide particle; and water, in which the polishing agent has a pH of 4 to 9.

FIELD OF THE INVENTION

The present invention relates to a polishing agent, a polishing method,and a liquid additive for polishing. More specifically, the presentinvention relates to a polishing agent for chemical mechanical polishingin the manufacture of a semiconductor integrated circuit, a polishingmethod using the polishing agent, and a liquid additive for polishingfor preparing a polishing agent.

BACKGROUND OF THE INVENTION

In recent years, with higher integration and higher functionality of asemiconductor integrated circuit, the development of microfabricationtechnology for achieving miniaturization and high density of asemiconductor element is advancing. In the manufacture of asemiconductor integrated circuit device (hereinafter, also referred toas a “semiconductor device”), in order to prevent a problem, forexample, that unevenness (difference in level) of a layer surfaceexceeds depth of focus of lithography and in turn, sufficient resolutionis not obtained, an interlayer insulating film, an embedded wiring, etc.have been conventionally flattened using Chemical Mechanical Polishing(hereinafter referred to as “CMP”). As the requirement for highdefinition and miniaturization of an element becomes severe, importanceis increasingly placed on high flattening by CMP.

Furthermore, in the recent manufacture of a semiconductor device, anisolation method using shallow trenches having a small element isolationwidth (Shallow Trench Isolation; hereinafter referred to as “STI”) isintroduced so as to proceed with higher miniaturization of asemiconductor element.

STI is a technique of forming a trench (groove) on a silicon substrateand embedding an insulating film in the trench, thereby forming anelectrically insulated element region. In STI, first, as illustrated inFIG. 1A, an element region of a silicon substrate 1 is masked with asilicon nitride film 2, etc., a trench 3 is formed on the siliconsubstrate 1, and an insulating layer such as silicon dioxide film 4 isthen deposited to fill the trench 3. Subsequently, the silicon dioxidefilm 4 on the silicon nitride film 2 defining a convex part is polishedand removed by CMP while leaving the silicon dioxide film 4 in thetrench 3 defining a concave part, and consequently, an element isolationstructure in which as illustrated in FIG. 1B, the silicon dioxide film 4is embedded in the trench 3 is obtained.

In CMP in STI, the progress of polishing can be stopped at the time ofexposure of a silicon nitride film by increasing a selection ratiobetween a silicon dioxide film and a silicon nitride film. A polishingmethod using the silicon nitride film as a stopper film in this way canprovide a smoother surface, compared with the conventional polishingmethod. In the recent CMP technology, it is important how high theabove-described selection ratio is.

A method for improving polishing properties of a polishing agent hasbeen proposed in response to such required characteristics. PatentDocument 1 discloses a polishing agent for a base material of asilicon-containing dielectric material, in which the polishing agentcontains, as an abrasive grain, a cerium oxide particle, etc. andcontains polyacrylic acid or ammonium polyacrylate.

With the polishing agent disclosed in Patent Document 1, the removalrate of silicon dioxide film may be assured of a high value to a certainextent, but since the removal rate of silicon nitride film is notsufficiently controlled, the selection ratio of silicon dioxide film tosilicon nitride film is not high enough. In turn, the flatness of thebase material obtained is unsatisfactory.

Patent Document 1: WO 2004/010487

SUMMARY OF THE INVENTION

The present invention has been made to solve the problems above, and anobject of the present invention is to provide a polishing agent and apolishing method, which are, for example, in CMP, particularly, in CMPin STI of a surface to be polished including a silicon oxide surface,capable of achieving a high selection ratio of silicon dioxide film tosilicon nitride film (the selection ratio means a ratio between theremoval rate of silicon dioxide film and the removal rate of siliconnitride film; hereinafter, also simply referred to as “selection ratio”)and good flatness by keeping the removal rate for a silicon nitride filmlow while maintaining a sufficiently high removal rate for a siliconoxide film such as silicon dioxide film.

A polishing agent according to the present invention includes:

a water-soluble polymer including a copolymer of a monomer (A) whichincludes at least one member selected from the group consisting of anunsaturated dicarboxylic acid, a derivative thereof, and salts of theunsaturated dicarboxylic acid and the derivative thereof and a monomer(B) other than the monomer (A), including an ethylenic double bond andno acidic group;

a cerium oxide particle; and

water, and

the polishing agent has a pH of 4 to 9.

A polishing method according to the present invention includes bringinga polishing pad into contact with a surface to be polished, whilesupplying a polishing agent to perform polishing by relative movementthereof, and the surface to be polished including a surface includingsilicon oxide of a semiconductor substrate is polished with thepolishing agent according to the present invention as the polishingagent.

A liquid additive for polishing according to the present invention is aliquid additive for preparing a polishing agent by being added to acerium oxide particle dispersion, the liquid additive includes:

a water-soluble polymer including a copolymer of a monomer (A) whichincludes at least one member selected from the group consisting of anunsaturated dicarboxylic acid, a derivative thereof, and salts of theunsaturated dicarboxylic acid and the derivative thereof and a monomer(B) other than the monomer (A), including an ethylenic double bond andno acidic group; and

water, and

the liquid additive has a pH of 4 to 9.

Incidentally, the “surface to be polished” as used in the presentinvention is a face to be polished of a polishing target and means, forexample, a surface. In the present description, the “surface to bepolished” encompasses also an intermediate-stage surface appearing on asemiconductor substrate in the process of manufacturing a semiconductordevice. The “silicon oxide” as used in the present invention isspecifically silicon dioxide, but the present invention is not limitedthereto and includes a silicon oxide other than silicon dioxide.

According to the polishing agent and polishing method of the presentinvention, the removal rate for a silicon nitride film is kept low whilemaintaining a sufficiently high removal rate for a silicon oxide film,for example, in CMP, particularly, in CMP in STI of a surface to bepolished including a silicon oxide surface, so that high selection ratioof silicon oxide to silicon nitride and good flatness can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views of a semiconductor substrate,illustrating the method of polishing by CMP in STI.

FIG. 2 is a view illustrating one example of the polishing apparatusthat can be used in the polishing method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is described below. However, thepresent invention is not limited to the following embodiment, and otherembodiments can be included in the scope of the present invention aslong as they conform to the gist of the present invention.

<Polishing Agent>

The polishing agent of the present invention has a pH of 4 to 9, andincludes: a water-soluble polymer including a copolymer of a monomer (A)which includes at least one member selected from the group consisting ofunsaturated dicarboxylic acid, a derivative thereof, and salts of theunsaturated dicarboxylic acid and the derivative thereof and a monomer(B) other than the monomer (A), including an ethylenic double bond andno acidic group; a cerium oxide particle; and water.

In the present description, the “water-soluble” means that “10 mg ormore of the polymer dissolves in 100 g of water at 25° C.”. In thecopolymer of monomer (A) and monomer (B), the unit based on monomer (A)and the unit based on monomer (B) are referred to as unit (A) and unit(B), respectively. The water-soluble polymer including a copolymer ofmonomer (A) and monomer (B) is simply referred to as “water-solublepolymer”. In the present description, the numerical range representedusing “to” includes the values on both sides thereof as lower and upperlimits. In the present description, the “(meth)acrylic acid” is ageneric term of “methacrylic acid” and “acrylic acid”.

In the case where the polishing agent of the present invention is used,for example, in CMP in STI of a surface to be polished including asilicon oxide film (e.g., silicon dioxide film), by virtue of a highremoval rate for a silicon oxide film and a sufficiently low removalrate for a silicon nitride film, a high selection ratio of silicon oxidefilm to silicon nitride film can be achieved and in turn, polishingproviding high flatness can be realized.

In the polishing agent of the present invention, the cerium oxideparticle functions as an abrasive grain. In the polishing agent of thepresent invention, it is considered that the water-soluble polymerincluding a copolymer of monomer (A) and monomer (B) dissolves in waterand functions to assist the action of the abrasive grain as describedbelow at a pH of 4 to 9, whereby the polishing agent of the presentinvention can exert the above-described remarkable effects.

The mechanism by which the polishing agent of the present inventionexerts the excellent polishing properties above is not clearly known,but it is thought that a carboxy group contained in the water-solublepolymer adsorbs to the cerium oxide particle surface and the surface tobe polished including a silicon nitride film, whereby the removal ratefor the silicon nitride film is reduced. Incidentally, the carboxylgroup is believed to function in the same manner as above even in theform of a salt. However, if the carboxy group is derivatized, itsfunction decreases. Accordingly, the monomer (A) preferably contains atleast a carboxy group or a salt of carboxy group.

Furthermore, in the copolymer constituting the water-soluble polymer,the unit (A) is hydrophilic, and the unit (B) is hydrophobic. It isconsidered that since the copolymer has a hydrophobic moiety and ahydrophilic moiety, the removal rate for a silicon nitride film isreduced while maintaining a high removal rate for a silicon oxide filmand, as a result, a high selection ratio is obtained.

The polishing agent of the present invention may contain othercomponents besides the water-soluble polymer, cerium oxide particle andwater, as long as the effects of the present invention are not impaired.In the following, respective components contained in the polishing agentof the present invention, such as cerium oxide particle, water-solublepolymer, water and other components, and the pH of the liquid aredescribed.

(Cerium Oxide Particle)

The cerium oxide particle contained in the polishing agent of thepresent invention is not particularly limited. For example, a ceriumoxide particle produced by the method described in JP-A-11-12561 orJP-A-2001-35818 can be used. More specifically, a cerium oxide particleobtained by adding an alkali to an aqueous cerium nitrate(IV) ammoniumsolution to prepare a cerium hydroxide gel and subjecting the gel tofiltration, cleaning and firing, or a cerium oxide particle obtained bypulverizing and then firing high-purity cerium carbonate and furtherpulverizing and classifying the fired product, can be used. In addition,a cerium oxide particle obtained by chemically oxidizing cerium(III)salt in a liquid, as described in JP-T-2010-505735, can also be used.

The average particle diameter of the cerium oxide particles ispreferably from 0.01 μm to 0.5 μm, more preferably from 0.03 μm to 0.3μm. If the average particle diameter of the cerium oxide particlesexceeds 0.5 μm, a polishing flaw such as scratch may be generated on thesurface to be polished. On the other hand, if the average particlediameter of the cerium oxide particles is less than 0.01 μm, not onlythe removal rate may decrease but also on account of a large percentageof the surface area per unit volume, the particles are susceptible tothe influence of surface state and likely to aggregate depending on theconditions such as pH and additive concentration.

The cerium oxide particle is present as an aggregated particle(secondary particle) resulting from aggregation of primary particles ina liquid and therefore, the preferable particle diameter of the ceriumoxide particle is expressed by an average secondary particle diameter.More specifically, the average particle diameter in the numerical rangeabove is usually an average secondary particle diameter. The averagesecondary particle diameter is measured by a particle size analyzer oflaser diffraction/scattering type, etc. by using a dispersion containingparticles dispersed in a dispersion medium such as deionized water.

The content ratio (concentration) of the cerium oxide particles ispreferably from 0.05 to 2.0 mass % relative to the total mass of thepolishing agent. In particular, the content ratio thereof is preferablyfrom 0.15 to 1.0 mass %. When the content ratio of the cerium oxideparticles is from 0.05 to 2.0 mass %, a sufficiently high removal ratefor a silicon oxide film is obtained. In addition, the viscosity of thepolishing agent is not too high, providing good handling properties.

As the cerium oxide particle, particles in the state of being previouslydispersed in a medium (hereinafter, referred to as “cerium oxideparticle dispersion”) may be used. In addition, a dispersant may beincorporated so as to obtain an optimal dispersion effect. The medium isnot particularly limited, but water may be preferably used.

(Water)

The polishing agent of the present invention contains water as a mediumfor dispersing cerium oxide particles and dissolving the later-describedwater-soluble polymer, etc. The kind of water is not particularlylimited, but deionized water, ultrapure water, ion-exchanged water, etc.is preferably used in consideration of the influence on thewater-soluble polymer, etc., prevention of contamination by impurities,and the influence on pH, etc.

(Water-Soluble Polymer)

The water-soluble polymer contained in the polishing agent of thepresent invention is incorporated so as to enhance the removal rate fora silicon oxide film and enhance the selection ratio of silicon dioxidefilm to silicon nitride film.

The water-soluble polymer includes a copolymer of the following monomer(A) and monomer (B). The monomer (A) includes at least one memberselected from the group consisting of an unsaturated dicarboxylic acid,a derivative thereof, and salts of the unsaturated dicarboxylic acid andthe derivative thereof. The monomer (B) includes a compound other thanthe monomer (A), including an ethylenic double bond and no acidic group.

The copolymer includes unit (A) based on the monomer (A) and unit (B)based on the monomer (B), in which each unit may be one kind or two ormore kinds and respective units may be connected to one another randomlyor blockwise.

As the unsaturated dicarboxylic acid according to the monomer (A), acompound having two carboxy groups per molecule and having an ethylenicdouble bond may be used without any particular limitation. Theunsaturated dicarboxylic acid may be a chain compound or a cycliccompound but is preferably a chain compound. The number of ethylenicdouble bonds in the unsaturated dicarboxylic acid is not limited but ispreferably 1 or 2, more preferably 1. The carbon number excluding thecarboxy group of the unsaturated dicarboxylic acid is preferably from 2to 5, more preferably 2 or 3, particularly preferably 2.

Examples of the unsaturated dicarboxylic acid include maleic acid,fumaric acid, itaconic acid, citraconic acid, mesaconic acid,2-allylmalonic acid, and isopropylidenesuccinic acid. Among these, atleast one member selected from the group consisting of maleic acid,fumaric acid and itaconic acid is preferred, and maleic acid is morepreferred in view of polymerizability.

The monomer (A) may be a derivative of an unsaturated dicarboxylic acid,a salt of an unsaturated dicarboxylic acid, or a salt of a derivative ofan unsaturated dicarboxylic acid. The salt of a derivative of anunsaturated dicarboxylic acid indicates a compound in which one carboxygroup of an unsaturated dicarboxylic acid is derivatized and the otherbecomes a salt.

Examples of the salt of an unsaturated dicarboxylic acid include analkali metal salt and an amine salt. Examples of the salt include asodium salt, a potassium salt, an ammonium salt, a monoethanolammoniumsalt, a diethanolammonium salt and atriethanolammonium salt, and anammonium salt is preferred in that contamination by a metal impurityneed not be considered.

Examples of the derivative of an unsaturated dicarboxylic acid includean acid anhydride, an ester derivative and an amide derivative, and thederivative is preferably an ester derivative. The ester or amide of anunsaturated dicarboxylic acid may be a derivative in which both or oneof carboxy groups of the unsaturated dicarboxylic acid is esterified oramidated.

The ester derivative of an unsaturated dicarboxylic acid is, forexample, a compound in which at least one carboxy group (—C(═O)—OH) ofthe unsaturated dicarboxylic acid becomes —C(═O)—O—R¹ (in which R¹ is amonovalent substituent). R¹ is preferably a saturated hydrocarbon grouphaving a carbon number of 1 to 50, which may have an oxygen atom betweencarbon-carbon atoms. R¹ is more preferably a saturated hydrocarbon grouphaving a carbon number of 2 to 30, still more preferably a carbon numberof 5 to 20, which may have an oxygen atom between carbon-carbon atoms.The saturated hydrocarbon group may be linear, branched or cyclic or maybe a linear or branched chain containing a cyclic structure.

The amide derivative of an unsaturated dicarboxylic acid is, forexample, a compound in which at least one carboxy group (—C(═O)—OH) ofthe unsaturated dicarboxylic acid becomes —C(═O)—NR²R³ (in which each ofR² and R³ is independently a hydrogen atom or a monovalent substituent).In the case where R² and R³ are a monovalent substituent, examples ofthe substituent include the same groups as those for R¹ described above.The preferred embodiment thereof is also the same as that of R¹.

The monomer (A) includes at least one member selected from the groupconsisting of an unsaturated dicarboxylic acid, a derivative thereof,and salts of the unsaturated dicarboxylic acid and the derivativethereof. In the case where the monomer (A) includes two or more of thesemembers, they may be a combination of different kinds of unsaturateddicarboxylic acids or a combination of an unsaturated dicarboxylic acidand a derivative thereof and/or their salts, with the unsaturateddicarboxylic acid being the same.

The monomer (A) preferably contains a salt of an unsaturateddicarboxylic acid. That is, in the copolymer, unit (A) based on themonomer (A) preferably has a salt of a carboxy group. When the monomer(A) contains a salt of an unsaturated dicarboxylic acid, the watersolubility of the copolymer is increased.

The monomer (A) preferably contains at least one member selected fromthe group consisting of an ester derivative in which at least a part ofan unsaturated dicarboxylic acid is esterified, and a salt thereof.Incidentally, the salt here is a salt of an ester derivative in which atleast a part of an unsaturated dicarboxylic acid is esterified. When themonomer (A) contains an ester derivative of an unsaturated dicarboxylicacid, the polishing agent of the present invention can have a higherselection ratio, and therefore, it is particularly preferred that themonomer (A) is a salt of an ester derivative in which a part of anunsaturated dicarboxylic acid is esterified.

In the preferred embodiment above, examples of the monomer (A) includean embodiment containing an ester derivative in which one or both ofcarboxy groups of an unsaturated dicarboxylic acid are esterified, anembodiment containing a compound in which one of the unsaturateddicarboxylic acid is esterified and the other becomes a salt, and anembodiment containing a mixture thereof. Furthermore, in the case wherethe monomer (A) described above is a salt, the monomer (A) may be anembodiment containing a combination of an ester derivative in which atleast a part of an unsaturated dicarboxylic acid is esterified, and asalt of an unsaturated dicarboxylic acid.

The expression “the monomer (A) contains a salt of an unsaturateddicarboxylic acid” as used in the present invention means that in thecopolymer of monomer (A) and monomer (B), the unit (A) contains a saltof a carboxy group. More specifically, the expression “the monomer (A)contains a salt of an unsaturated dicarboxylic acid” encompasses both acase where the monomer (A) is a salt at the time of production of thecopolymer, and a case where after obtaining the copolymer, a carboxygroup of unit (A) is turned into a salt.

Describing the monomer (A) by reference, for example, to maleic acidthat is suitable as the unsaturated dicarboxylic acid, the monomer (A)preferably contains at least one member selected from the groupconsisting of a maleic acid monoester, a maleic acid diester, and a saltof a maleic acid monoester. In this case, the monomer (A) may contain amaleic acid or may contain a maleic acid salt. It is more preferable forthe monomer (A) to contain a salt of a maleic acid monoester or containa maleic acid ester and a maleic acid salt in combination, and it isparticularly preferable to contain a salt of a maleic acid monoester.

In the monomer (A) as whole, that is, in unit (A) in the copolymer, theratio between an esterified carboxy group and a salt of carboxy group ispreferably from 1:9 to 9:1, particularly preferably 5:5. Incidentally,when a carboxy group forms a salt in the monomer (A), a carboxy group(—COOH) is not present in the monomer (A) due to manufacturing reason.

The monomer (B) is a compound other than the monomer (A), including anethylenic double bond and no acidic group. The monomer (B) may be achain compound or a cyclic compound containing a ring structure and ispreferably a cyclic compound containing a ring structure. When themonomer (B) contains a ring structure, the storage stability of theobtained polishing agent is increased.

In the case where the monomer (B) contains a ring structure, unit (B) inthe copolymer preferably has a ring structure in the side chain. In thiscase, the ring is an aliphatic ring or an aromatic ring and ispreferably a 5-membered ring or a 6-membered ring. The number ofethylenic double bonds is not particularly limited but includes a rangeof 1 to 5 and is preferably 1 or 2, particularly preferably 1.Furthermore, in the case where the monomer (B) contains a ringstructure, the ring may be a heterocycle containing, in the skeleton, anelement other than carbon atom, for example, an oxygen atom or anitrogen atom, and the hydrogen atom bonded to the ring may besubstituted by a substituent except for an acidic group. Examples of thesubstituent include a hydrocarbon group having a carbon number of 1 to30, an oxy group (—O—R), an oxo group (═O), a carbonyl group (—CO—R), anamino group (—NH—R), an imino group (═N—R), an azo group (—N═N—R), adiazo group (—N≡N—R), a halogen group, a thio group (—S—R), and aphosphono group. Here, R is a monovalent organic group.

In the case where the monomer (B) is a chain compound, the number ofethylenic double bonds is not particularly limited but includes a rangeof 1 to 5 and is preferably 1 or 2, particularly preferably 1. The chaincompound is a linear or branched chain, and the carbon number thereof isnot particularly limited but includes a range of 2 to 30 and ispreferably from 2 to 10.

Examples of the monomer (B) containing a ring structure include amonocyclic olefin such as cyclobutane, cyclopentene, cyclohexene,cycloheptene and cyclooctene, or a derivative thereof, a cyclicconjugated diene such as cyclopentadiene, cyclohexadiene,cycloheptadiene and cyclooctadiene, or a derivative thereof; apolycyclic olefin such as norbornene, dicyclopentadiene, tricyclodecene,tetracyclododecene and hexacycloheptadecene, or a derivative thereof; avinyl-alicyclic hydrocarbon such as vinylcyclobutane, vinylcyclobutene,vinylcyclopentane, vinylcyclopentene, vinylcyclohexane, vinylcyclohexene, vinyl cycloheptane, vinylcycloheptene, vinylcyclooctane,vinylcyclooctene, N-vinylpyrrolidone, N-vinylcarbazole and4-vinylpyridine, or a derivative thereof; and a vinyl-aromatic monomersuch as styrene, methyl styrene, vinyltoluene, p-tert-butyl styrene,chloromethylstyrene, o-(or p-, m-)hydroxystyrene, and o-(or p-,m-)hydroxyphenyl acrylate, or a derivative thereof.

Examples of the monomer (B) that is a chain compound include an olefinsuch as ethylene, propylene, butene, pentene, hexene, heptene, octene,nonene, decene, isopropylene, isobutene, isopentene, isohexene,isoheptene, isooctene, isononene and isodecene, or a derivative thereof,an aliphatic conjugated diene such as butadiene, 1,3-butadiene,isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene, or a derivativethereof, a (meth)acrylic acid ester such as methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl(meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,n-octyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate and hydroxypropyl(meth)acrylate, or a derivative thereof, an ethylenically unsaturatedcarboxylic acid hydroxyalkyl ester such as β-hydroxyethyl acrylate,β-hyddroxypropyl acrylate and β-hydroxyethyl methacrylate, or aderivative thereof; an unsaturated carboxylic acid glycidyl ester suchas glycidyl acrylate and glycidyl methacrylate, or a derivative thereof,a vinyl compound such as acrolein and allyl alcohol, or a derivativethereof, an ethylenically unsaturated nitrile such as acrylonitrile andmethacrylonitrile, or a derivative thereof; and an ethylenicallyunsaturated carboxylic acid amide such as acrylamide, methacrylamide,N-methylolacrylamide and diacetone acrylamide, or a derivative thereof.

Among these, as the monomer (B), styrene, N-vinylpyrrolidone,4-vinylpyridine, heptene, octene, nonene, and isobutene are preferred,styrene, N-vinylpyrrolidone and 4-vinylpyridine are more preferred, andstyrene is particularly preferred.

Incidentally, the monomer (B) may be one kind or two or more kinds. Forexample, in the case where the monomer (B) contains styrene, the monomer(B) may contain a monomer other than styrene, such asN-vinylpyrrolidone, heptene, octene, nonene and isobutene. In this case,the content ratio of styrene is preferably from 50 to 100 mol %, morepreferably from 70 to 100 mol %, particularly preferably 100 mol %,relative to the whole of the monomer (B).

Each of the monomer (A) and monomer (B) in the copolymer has beendescribed. The monomer (A) and the monomer (B) can be combined byappropriately selecting one kind or two or more kinds for each monomer.The preferable combination is a combination of preferable monomersrecited above for the monomer (A) and the monomer (B), respectively. Inthe copolymer used for the polishing agent of the present invention, acombination where the unsaturated dicarboxylic acid in the monomer (A)contains maleic acid and the monomer (B) contains styrene isparticularly preferred.

In the copolymer, the ratio of the monomer (A) to the monomer (B), thatis, the ratio of unit (A) to unit (B), is not particularly limited.Considering the balance between hydrophilicity of unit (A) andhydrophobicity of unit (B), the molar ratio of unit (A) to unit (B)includes a range from 10:90 to 90:10, and the molar ratio thereof ispreferably from 20:80 to 80:20, more preferably from 40:60 to 60:40.

The weight average molecular weight of the copolymer is preferably from500 to 1,000,000, more preferably from 1,000 to 20,000, still morepreferably from 2,000 to 10,000. When the weight average molecularweight of the copolymer is 500 or more, the copolymer can be stably keptin a state of being adsorbed to a cerium oxide particle surface and asurface to be polished including a silicon oxide film. When the averagemolecular weight of the copolymer is 1,000,000 or less, the handlingproperties, etc. are good. Unless otherwise indicated, the weightaverage molecular weight (hereinafter, also denoted by “Mw”) as used inthe present description is a weight average molecular weight measured bygel permeation chromatograph (GPC).

The water-soluble polymer includes a copolymer of monomer (A) andmonomer (B), in which the copolymer is one kind or two or more kinds. Asfor the acid value and weight average molecular weight of thewater-soluble polymer, the same ranges as those of the acid value andweight average molecular weight of the copolymer above are preferred.

The content ratio (concentration) of the water-soluble polymer ispreferably from 0.001 to 10.0 mass %, more preferably from 0.01 to 5.0mass %, relative to the total mass of the polishing agent, because ahigh removal rate for a silicon oxide film as well as a high selectionratio are obtained. In addition, the content ratio thereof is still morepreferably from 0.05 to 2.0 mass %, because a sufficiently high removalrate for a silicon oxide film as well as a higher selection ratio areobtained.

(pH)

The pH of the polishing agent of the present invention is from 4 to 9.When the pH of the polishing agent is 9 or less, the effect of reducingthe removal rate for a silicon nitride film and enhancing the selectionratio is sufficiently obtained. In addition, when the pH of thepolishing agent is 4 or more, the removal rate for a silicon oxide filmis enhanced. The pH of the polishing agent is more preferably from 5 to9, particularly preferably from 6 to 8.

The polishing agent of the present invention may contain a pH regulatorso as to adjust the pH to a predetermined value. The pH regulator ispreferably an acid, and various inorganic acids or organic acids orsalts thereof may be used. The inorganic acid is not particularlylimited, but examples thereof include nitric acid, sulfuric acid,hydrochloric acid, and phosphoric acid. The organic acid is notparticularly limited, but examples thereof include carboxylic acid,sulfonic acid, and phosphoric acid. Among these, carboxylic acid ispreferred. The carboxylic acid may be any appropriate carboxylic acid,but more preferable carboxylic acids are exemplified below.

Carboxylic acid (monocarboxylic acid, polycarboxylic acid) having anitrogen-containing heterocyclic group: 2-pyridinecarboxylic acid,3-pyridinecarboxylic acid, 4-pyridinecarboxylic acid,2,3-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid,2,5-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid,3,4-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid,pyrazinecarboxylic acid, 2,3-pyrazinedicarboxylic acid,2-quinolinecarboxylic acid, pyroglutamic acid, picoline acid, andDL-pipecolic acid.

Carboxylic acid having a cyclic compound except for nitrogen:2-furancarboxylic acid, 3-furancarboxylic acid,tetrahydrofuran-2-carboxylic acid, andtetrahydrofuran-2,3,4,5-tetracarboxylic acid.

Amino group-containing carboxylic acid (e.g., amino acid): alanine,glycine, glycylglycine, aminobutyric acid, N-acetylglycine,N,N-di(2-hydroxyethyl)glycine, N-(tert-butoxycarbonyl)glycine, proline,trans-4-hydroxy-L-proline, phenylalanine, sarcosine, hydantoic acid,creatine, N-[tris(hydroxymethyl)methyl]glycine, glutamic acid, andaspartic acid.

Hydroxyl group-containing carboxylic acid (e.g., hydroxycarboxylicacid): lactic acid, malic acid, citric acid, tartaric acid, glycolicacid, gluconic acid, salicylic acid, 2-hydroxyisobutyric acid, glycericacid, 2,2-bis(hydroxymethyl)propionic acid, and2,2-bis(hydroxymethyl)butyric acid.

Ketone group-containing carboxylic acid (keto acid): pyruvic acid,acetoacetic acid, and levulinic acid.

Cyclic carboxylic acid: cyclopentanecarboxylic acid,cyclohexanecarboxylic acid, cycloheptanecarboxylic acid, andcyclohexylcarboxylic acid.

Polycarboxylic acids other than those described above: oxalic acid,malonic acid, succinic acid, fumaric acid, maleic acid, glutaric acid,adipic acid, and phthalic acid.

The above-described inorganic acid or organic acid may also be used as asalt. As for the salt, an alkali metal salt, an amine salt, etc. may beused. Specifically, examples of the salt include a sodium salt, apotassium salt, an ammonium salt, a monoethanolammonium salt, adiethanolammonium salt, and a triethanolammonium salt.

In addition, as a pH regulator, various basic compounds may be added tothe polishing agent of the present invention. The basic compound ispreferably water-soluble but is not particularly limited thereto. Thebasic compound that can be used includes, for example, ammonia,potassium hydroxide, a quaternary ammonium hydroxide such astetramethylammonium hydroxide (hereinafter, referred to as TMAH) andtetraethylammonium hydroxide, and an organic amine such asmonoethanolamine (hereinafter, referred to as MEA) and ethylene diamine.

In the polishing agent of the present invention, an aggregationinhibitor or a dispersant may be incorporated, other than the componentsdescribed above.

The dispersant is incorporated so as to stably disperse cerium oxideparticles in a dispersion medium such as deionized water. Examples ofthe dispersant include anionic, cationic, nonionic and amphotericsurfactants, and anionic, cationic, nonionic and amphoteric polymercompounds, and one of these or two or more thereof may be incorporated.

Furthermore, in the polishing agent of the present invention, alubricant, a tackifier or viscosity regulator, a preservative, etc. maybe appropriately incorporated, if desired.

For the convenience of storage or transportation of the polishing agentof the present invention, a cerium oxide particle dispersion(hereinafter, referred to as “dispersion”) and an aqueous solutionobtained by dissolving the water-soluble polymer in water (liquidadditive for polishing) may be separately prepared as two liquids and bemixed at the time of use.

<Liquid Additive for Polishing>

The liquid additive for polishing of the present invention is a liquidadditive for preparing a polishing agent by being added to a ceriumoxide particle dispersion, in which the liquid additive has a pH of 4 to9, and includes: a water-soluble polymer including a copolymer of amonomer (A) which includes at least one member selected from the groupconsisting of an unsaturated dicarboxylic acid, a derivative thereof,and salts of the unsaturated dicarboxylic acid and the derivativethereof and a monomer (B) other than the monomer (A), including anethylenic double bond and no acidic group; and water. When a method ofusing this liquid additive for polishing in the preparation of thepolishing agent and adding it to a cerium oxide particle dispersion isemployed, the convenience of storage or transportation of the polishingagent can be enhanced.

Respective components contained in the liquid additive for polishing ofthe present invention, i.e., a water-soluble polymer and water, and thepH of the liquid are the same as those described for respectivecomponents contained in the polishing agent above and the pH of theliquid.

In the liquid additive for polishing of the present invention, thecontent ratio (concentration) of the water-soluble polymer is preferablyfrom 0.001 to 30 mass %, more preferably from 0.01 to 20 mass %, stillmore preferably from 0.1 to 10 mass %, relative to the entire liquidadditive.

In the cerium oxide particle dispersion to which the liquid additive isadded, the content ratio of the cerium oxide particle in the liquid ispreferably from 0.2 to 40 mass %, more preferably from 1 to 20 mass %,still more preferably from 5 to 10 mass %.

The liquid additive for polishing of the present invention is added tothe cerium oxide particle dispersion, so that a polishing agent capableof achieving high selection ratio and flatness by keeping the removalrate for a silicon nitride film low while maintaining a high removalrate for a silicon oxide film can be obtained.

Incidentally, in the case of preparing the polishing agent by mixing twoseparate liquids, i.e., the cerium oxide particle dispersion and theliquid additive for polishing of the present invention, theconcentration of the cerium oxide particle in the dispersion and theconcentration of the water-soluble polymer in the liquid additive forpolishing may be enriched to be from 2 to 100 times higher than theconcentrations in using the polishing agent and be diluted topredetermined concentrations at the time of use. More specifically, forexample, in the case where both the concentration of the cerium oxideparticle in the dispersion and the concentration of the water-solublepolymer in the liquid additive are enriched 10 times, 10 parts by massof the dispersion, 10 parts by mass of the liquid additive forpolishing, and 80 parts by mass of water are mixed and stirred, and theresulting mixture is used as the polishing agent.

<Preparation Method of Polishing Agent>

In order to prepare the polishing agent of the present invention, amethod of adding the water-soluble polymer to a dispersion in whichcerium oxide particles are dispersed in water such as deionized water orion-exchanged water, followed by mixing, is used. After the mixing, themixture is stirred for a predetermined time with a stirrer, etc., and auniform polishing agent is thereby obtained. In addition, after themixing, the mixture may be treated in an ultrasonic disperser to obtaina better dispersion state.

The polishing agent of the present invention need not necessarily besupplied to the polishing site after previously mixing all of theconstituent polishing components. The polishing components may be mixedto formulate the composition of the polishing agent when it is suppliedto the polishing site.

For the convenience of storage or transportation of the polishing agentof the present invention, as described above, a cerium oxide particledispersion and an liquid additive for polishing may be separatelyprepared as two liquids and be mixed at the time of use. The method forpreparing the polishing agent by mixing two separate liquids, i.e., thedispersion and the liquid additive for polishing, is describedhereinabove.

<Polishing Method>

The polishing method according to an embodiment of the present inventionis a method of bringing a surface to be polished of a polishing targetinto contact with a polishing pad while supplying the above-describedpolishing agent, and performing polishing by relative movement betweenthose two members. Here, the surface to be polished which is to besubjected to polishing is, for example, a surface including a faceincluding silicon dioxide of a semiconductor substrate. Preferableexamples of the semiconductor substrate include a substrate for theabove-described STI. The polishing agent of the present invention iseffective also in polishing for flattening of an interlayer insulatingfilm between multilayer interconnections in the manufacture of a semiconductor device.

The silicon dioxide film in a substrate for STI includes a so-calledPE-TEOS film deposited by a plasma CVD method using tetraethoxysilane(TEOS) as a raw material. In addition, as the silicon dioxide film, aso-called HDP film deposited by a high-density plasma CVD method may bementioned. Furthermore, a HARP film or FCVD film deposited by other CVDmethods, and an SOD film formed by spin coating may also be used. As thesilicon nitride film, a film deposited by a low-pressure CVD method orplasma CVD method using silane or dichlorosilane and ammonia as rawmaterials, and a film deposited by an ALD method may be mentioned.

In the polishing method according to an embodiment of the presentinvention, a known polishing apparatus can be used. FIG. 2 is a viewillustrating one example of the polishing apparatus that can be used inthe polishing method of the present invention.

The polishing apparatus 20 has a polishing head 22 for holding asemiconductor substrate 21 such as STI substrate, a polishing platen 23,a polishing pad 24 attached to a surface of the polishing platen 23, anda polishing agent supply pipe 26 for supplying a polishing agent 25 tothe polishing pad 24. The apparatus is configured to bring the surfaceto be polished of the semiconductor substrate 21 held in the polishinghead 22 into contact with the polishing pad 24 while supplying thepolishing agent 25 from the polishing agent supply pipe 26 and performpolishing by relative rotational movement between the polishing head 22and the polishing platen 23. Incidentally, the polishing apparatus usedin the embodiment of the present invention is not limited to such astructure.

The polishing head 22 may perform not only rotational movement but alsolinear movement. In addition, the polishing platen 23 and the polishingpad 24 may have a size equivalent to or smaller than that of thesemiconductor substrate 21. In this case, the polishing head 22 and thepolishing platen 23 are preferably moved relatively so that the entiresurface of the surface to be polished of the semiconductor substrate 21can be polished. Furthermore, the polishing platen 23 and the polishingpad 24 may not perform rotational movement and may move, for example, inone direction by a belt system.

The polishing conditions of the polishing apparatus 20 are notparticularly limited, but when the polishing head 22 is pressed againstthe polishing pad 24 by applying a load, the polishing pressure can bemore increased, and the removal rate can be enhanced. The polishingpressure is preferably on the order of 0.5 to 50 kPa, and in view ofuniformity of the removal rate within the surface to be polished of thesemiconductor substrate 21, flatness and prevention of a polishingdefect such as scratch, the polishing pressure is more preferably on theorder of 3 to 40 kPa. The rotation speed of the polishing platen 23 andthe polishing head 22 is preferably on the order of 50 to 500 rpm, butthe present invention is not limited thereto. The supply amount of thepolishing agent 25 is appropriately adjusted according to thecomposition of polishing agent, the above-described polishingconditions, etc.

As the polishing pad 24, a pad made of nonwoven fabric, foamedpolyurethane, porous resin, nonporous resin, etc. may be used. In orderto accelerate the supply of the polishing agent 25 to the polishing pad24 or allow a certain amount of the polishing agent 25 to stay on thepolishing pad 24, the surface of the polishing pad 24 may be processedto form a groove, for example, in a lattice-like, concentric or spiralmanner. In addition, a pad conditioner may be brought into contact withthe surface of the polishing pad 24, if desired, to perform polishingwhile conditioning the surface of the polishing pad 24.

According to the polishing method of the present invention, in a CMPtreatment at the time of manufacture of a semiconductor device, such asflattening of an interlayer insulating film or flattening of aninsulating film for STI, a surface to be polished including siliconoxide (e.g., silicon dioxide) can be polished at a high removal rate andmoreover, a high selection ratio of a silicon oxide film to a siliconnitride film can be realized, so that high flatness can be achieved.

EXAMPLES

The present invention is specifically described below by reference toworking examples and comparative examples, but the invention should notbe construed as being limited to those examples. In following Examples,unless otherwise indicated, “%” means mass %. The characteristic valueswere measured and evaluated by the following methods. Examples 1 to 14are working examples, and Examples 15 to 18 are comparative examples.

[pH]

The pH was measured using a pH meter, HM-30R, manufactured by DKK-TOACorporation.

[Average Secondary Particle Diameter]

The average secondary particle diameter was measured using a laserscattering/diffraction particle size distribution analyzer (manufacturedby Horiba, Ltd., device name: LA-920).

[Polishing Properties]

The polishing properties were evaluated using a full automatic CMPpolishing apparatus, FREX300 (manufactured by EBARA CORPORATION). As thepolishing pad, a two-layer pad (IC-1570, manufactured by Rodel, Inc.)was used, and for the conditioning of polishing pad, a diamond padconditioner (trade name: A165, manufactured by 3M Company) was used. Thepolishing conditions were a polishing pressure of 21 kPa, a rotationspeed of the polishing platen of 100 rpm, and a rotation speed of thepolishing head of 102 rpm. Unless otherwise indicated, the supply rateof the polishing agent was set to 250 ml/min.

As a polishing target (an object to be polished) for the evaluation ofremoval rate and selection ratio, a silicon dioxide film-attached waferin which a silicon dioxide film was deposited on a 12-inch silicon waferby plasma CVD using tetraethoxysilane or monosilane as a raw material,was used, and in addition, a silicon nitride film-attached wafer inwhich a silicon nitride film was deposited in the same manner as aboveby CVD, was used (hereinafter, these wafers are referred to as “blanketwafer”).

Incidentally, for the measurement of the film thickness of each of thesilicon dioxide film and silicon nitride film deposited on the blanketsubstrate, a thickness meter, VM-3210, manufactured by SCREENSemiconductor Solutions Co., Ltd. was used. The removal rate for each ofthe silicon dioxide film and the silicon nitride film was calculated bydetermining the difference between the film thickness before polishingof the blanket substrate and the film thickness after polishing for 1minute. The average value (nm/min) of the removal rate, obtained fromthe removal rates at 49 in-plane points of the substrate, was used as anindicator for evaluation of the removal rate. Furthermore, the ratiobetween the removal rate for a silicon dioxide film and the removal ratefor a silicon nitride film (removal rate for silicon dioxidefilm/removal rate for silicon nitride film) was calculated as aselection ratio.

The results shown together in Table 1 demonstrate, based on Examples 1to 14 as working examples and Examples 15 to 18 as comparative examples,that when a blanket wafer is polished with the polishing agent of thepresent invention, a high removal rate for silicon dioxide is obtainedand the polishing agent has a very high selection ratio of silicondioxide to silicon nitride.

(Water-Soluble Polymer and Water-Soluble Polymer of Comparative Example)

The molecular configurations of the water-soluble polymer including acopolymer of monomer (A) and monomer (B) (water-soluble polymer forworking example) and the water-soluble polymer for comparative example,which are used in each of the following Examples, are described below.

(Water-Soluble Polymer for Example)

Water-Soluble Polymer A:

A 50:50 (molar ratio) copolymer of a maleic acid alkyl (the alkyl is alinear alkyl having a carbon number of 19 to 20) ester ammonium salt asthe monomer (A) and styrene as the monomer (B); Mw: 3,000.

Water-Soluble Polymer B:

A 50:50 (molar ratio) copolymer of a maleic acid 2-butoxyethyl esterammonium salt as the monomer (A) and styrene as the monomer (B); Mw:7,000.

Water-Soluble Polymer C:

A copolymer of an ammonium maleate salt as the monomer (A) and octene(C₈H₁₆) as the monomer (B).

Water-Soluble Polymer D:

A copolymer of an ammonium maleate salt as the monomer (A) andisobutylene as the monomer (B); Mw: from 55,000 to 65,000.

Water-Soluble Polymer E:

A copolymer of an ammonium maleate salt as the monomer (A) and styreneas the monomer (B); Mw: 600,000.

Water-Soluble Polymer F:

A 33:66 (molar ratio) copolymer of a maleic acid 1-propyl ester (assumedadduct) ammonium salt as the monomer (A) and styrene as the monomer (B);Mw: 9,000.

In all of the monomer (A) above, the ratio between ester and ammoniumsalt in the maleic acid ester ammonium salt is 1:1.

(Water-Soluble Polymer for Comparative Example)

Water-Soluble Polymer G:

A homopolymer of an ammonium acrylate salt; Mw: 5,000.

Water-Soluble Polymer H:

A homopolymer of maleic acid.

Example 1

Two kinds of cerium oxide particles differing in the average particlediameter and ammonium polyacrylate having a molecular weight of 5,000 asa dispersant were added to deionized water to provide a mass ratio of100:0.7, mixed under stirring, and subjected to ultrasonic dispersionand filtering to prepare a cerium oxide particle dispersion having acerium oxide particle concentration of 10% and a dispersantconcentration of 0.07%. Incidentally, the average secondary particlediameter of cerium oxide particles was 0.11 μm (hereinafter, referred toas Cerium Oxide Dispersion A) and 0.18 μm (hereinafter, referred to asCerium Oxide Dispersion B).

Next, Water-Soluble Polymer A was added to deionized water to provide aconcentration of 0.005% relative to the total amount of the polishingagent, Cerium Oxide Dispersion A was added to provide a cerium oxideparticle concentration of 0.25% relative to the total amount of thepolishing agent, and the pH was adjusted to 7.0 by further adding nitricacid to obtain Polishing Agent (1).

Examples 2 to 8, 10, and 12 to 14

Polishing Agents (2) to (8), (10), and (12) to (14) were obtained byadding the same Cerium Oxide Dispersion A and water-soluble polymer asin Example 1 to deionized water each to provide the concentration shownin Table 1 and after stirring, further adding a pH regulator to adjustthe pH as shown in Table 1.

Examples 9 and 11

Polishing Agents (9) and (11) were obtained by adding Cerium OxideParticle Dispersion B and the water-soluble polymer to deionized watereach to provide the concentration shown in Table 1 and after stirring,further adding a pH regulator to adjust the pH as shown in Table 1.

Example 15

Polishing Agent (15) was obtained by adding the same Cerium OxideDispersion A as in Example 1 to deionized water to provide theconcentration shown in Table 1, followed by stirring, but not adding awater-soluble polymer.

Examples 16 to 18

Polishing Agents (16) to (18) were obtained by adding the same CeriumOxide Dispersion A and water-soluble polymer as in Example 1 todeionized water each to provide the concentration shown in Table 1 andafter stirring, further adding a pH regulator to adjust the pH as shownin Table 1.

The polishing properties (removal rate for silicon dioxide film, removalrate for silicon nitride film, and selection ratio) of each of PolishingAgents (1) to (18) obtained in Examples 1 to 18 were measured by theabove-described methods. Incidentally, for the measurement of polishingproperties, a blanket wafer was used as the polishing target (the objectto be polished).

TABLE 1 Average Secondary Particle Diameter Water- Removal Removal ofCerium Cerium Oxide Soluble Rate for Rate for Oxide Particle PolymerSilicon Silicon Particle Concentration Kind of Concentration Oxide FilmNitride Film Selection [μm] [mass %] Water-Soluble Polymer [mass %] pHregulator pH [nm/min] [nm/min] Ratio Example 1 0.11 0.25 Water-SolublePolymer A  0.005 nitric acid 7.0 145 6.2 23 Example 2 0.11 0.25Water-Soluble Polymer A 0.01 nitric acid 7.0 121 4.0 30 Example 3 0.110.25 Water-Soluble Polymer A 0.05 nitric acid 5.5 127 4.1 31 Example 40.11 1.00 Water-Soluble Polymer A 1.20 nitric acid 6.3 265 5.4 49Example 5 0.11 0.25 Water-Soluble Polymer A 0.05 nitric acid 8.6 96 4.223 Example 6 0.11 0.25 Water-Soluble Polymer B 0.10 nitric acid 4.3 661.1 60 Example 7 0.11 0.25 Water-Soluble Polymer B 0.40 nitric acid 7.094 1.0 94 Example 8 0.11 0.25 Water-Soluble Polymer B 0.10 nitric acid8.0 127 2.4 53 Example 9 0.18 0.50 Water-Soluble Polymer A 0.30 nitricacid 6.5 254 3.9 65 Example 10 0.11 0.25 Water-Soluble Polymer C 0.06nitric acid 6.4 152 3.1 49 Example 11 0.18 0.25 Water-Soluble Polymer D0.01 nitric acid 6.1 167 3.3 51 Example 12 0.11 0.25 Water-SolublePolymer E 0.05 nitric acid 7.0 84 3.1 27 Example 13 0.11 0.25Water-Soluble Polymer A 0.05 nitric acid 7.0 120 3.0 40 Example 14 0.110.25 Water-Soluble Polymer F 0.20 nitric acid 8.0 230 3.2 72 Example 150.11 0.25 — — — 7.0 329 27.0 12 Example 16 0.11 0.25 Water-SolublePolymer G 0.05 nitric acid 5.3 103 8.5 12 Example 17 0.11 0.25Water-Soluble Polymer H 0.02 potassium 5.0 86 6 13 hydroxide Example 180.11 0.25 Water-Soluble Polymer A 0.05 potassium 10.0 92 8 12 hydroxide[Storage Stability]

A polishing agent prepared by adding the water-soluble polymer shown inTable 2 below to deionized water to provide a concentration of 0.2%relative to the total amount of the polishing agent, adding Cerium OxideDispersion A to provide a cerium oxide particle concentration of 1.0%relative to the total amount of the polishing agent, and further addingnitric acid to adjust the pH to a predetermined value was stored at roomtemperature of around 25° C., and the change over time of the pH waschecked, thereby effecting the test of storage stability. The resultsare shown in Table 2. As compared to the pH of the polishing agent onthe day of the preparation, in the case where the pH thereof was notchanged after 7 days, the storage stability of the polishing agent wasevaluated as “A”. On the other hand, in the case where the change in thepH of the polishing agent after 7 days was 0.5 or more, the storagestability of the polishing agent was evaluated as “B”.

TABLE 2 Average Cerium Water- Secondary Oxide Kind of Soluble ParticleParticle Water- Polymer pH Diameter Concentration Soluble Concentrationon the after 1 after 7 Storage [μm] [mass %] Polymer [mass %] day daydays Stability 0.11 1 Water- 0.2 4.1 4.1 4.1 A Soluble Polymer A 0.11 1Water- 0.2 4.0 4.0 4.0 A Soluble Polymer E 0.11 1 Water- 0.2 4.0 5.8 5.2B Soluble Polymer C 0.11 1 Water- 0.2 3.9 5.2 5.2 B Soluble Polymer D

Tables 1 and 2 reveal the followings. Namely, it is seen that whenpolishing is performed using Polishing Agents (1) to (14) of Examples 1to 14 each having a pH of 4 to 9 and including: a water-soluble polymerincluding a copolymer of a monomer (A) which includes at least onemember selected from the group consisting of an unsaturated dicarboxylicacid, a derivative thereof, and salts of the unsaturated dicarboxylicacid and the derivative thereof and a monomer (B) other than the monomer(A), including an ethylenic double bond and no acidic group; a ceriumoxide particle; and water, a high removal rate for a silicon dioxidefilm is obtained and the selection ratio of silicon dioxide film tosilicon nitride film is high. In the case where the monomer (A) is anester derivative, the selection ratio can be raised. In the case wherethe monomer (B) is a cyclic structure, the storage stability can beenhanced.

On the other hand, it is seen that Polishing Agent (15) not containing awater-soluble polymer which is a copolymer of the monomer (A) and themonomer (B) causes a decrease in the selection ratio of silicon dioxidefilm to silicon nitride film, compared with a case using PolishingAgents (1) to (14) of Examples 1 to 14 which are working examples.

In addition, it is seen that Polishing Agents (16) and (17) each using awater-soluble polymer which is close in terms of structure but is not acopolymer of the monomer (A) and the monomer (B) also cause a decreasein the selection ratio of silicon dioxide film to silicon nitride film,compared with a case using Polishing Agents (1) to (14) of Examples 1 to14. Furthermore, it is seen that also when Polishing Agent (18)containing a water-soluble polymer which is a copolymer of the monomer(A) and the monomer (B) but having a pH of 10 or more is used, theselection ratio of silicon dioxide film to silicon nitride filmdecreases, compared with a case using Polishing Agents (1) to (14) ofExamples 1 to 14.

The present application is based on Japanese patent application No.2017-215520 filed on Nov. 8, 2017, and the contents of which areincorporated herein by reference.

According to the present invention, for example, in CMP of a surface tobe polished including a surface including silicon oxide, a highselection ratio of silicon dioxide film to silicon nitride film can beachieved by keeping the removal rate for a silicon nitride film lowwhile maintaining a sufficiently high removal rate for a silicon oxidefilm. The polishing agent and polishing method of the present inventionare therefore suitable for flattening an insulating film for STI at thetime of manufacture of a semiconductor device.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1: Silicon substrate, 2: silicon nitride film, 3: trench, 4: silicondioxide film, 20: polishing apparatus, 21: semiconductor substrate, 22:polishing head, 23: polishing platen, 24: polishing pad, 25: polishingagent, and 26: polishing agent supply pipe.

What is claimed is:
 1. A polishing agent comprising: a water-soluble polymer comprising a copolymer of a monomer (A) which comprises at least one member selected from the group consisting of an unsaturated dicarboxylic acid, a derivative thereof, and salts of the unsaturated dicarboxylic acid and the derivative thereof and a monomer (B) other than the monomer (A), comprising an ethylenic double bond and no acidic group; a cerium oxide particle; a pH regulator; and water, wherein: the polishing agent has a pH of 4 to 8.6; and at least a part of the unsaturated dicarboxylic acid is esterified.
 2. The polishing agent according to claim 1, wherein the unsaturated dicarboxylic acid comprises at least one member selected from the group consisting of maleic acid, itaconic acid and fumaric acid.
 3. The polishing agent according to claim 1, wherein the monomer (B) comprises a cyclic compound containing a 5-membered ring or a 6-membered ring.
 4. The polishing agent according to claim 1, wherein the pH regulator is an acid.
 5. The polishing agent according to claim 1, wherein, in the copolymer, a unit based on the monomer (A) has a salt of a carboxy group.
 6. The polishing agent according to claim 1, wherein the monomer (B) comprises at least one member selected from the group consisting of styrene, N-vinylpyrrolidone and 4-vinylpyridine.
 7. The polishing agent according to claim 6, wherein the unsaturated dicarboxylic acid comprises maleic acid, and the monomer (B) comprises styrene.
 8. The polishing agent according to claim 6, wherein the monomer (A) comprises at least one member selected from the group consisting of an ester derivative in which at least a part of maleic acid is esterified, and a salt thereof.
 9. The polishing agent according to claim 1, containing the water-soluble polymer in an amount of from 0.001 to 10.0 mass %.
 10. The polishing agent according to claim 1, containing the water-soluble polymer in an amount of from 0.01 to 5.0 mass %.
 11. The polishing agent according to claim 1, containing the cerium oxide particle in an amount of from 0.05 to 2.0 mass %.
 12. A polishing method comprising bringing a polishing pad into contact with a surface to be polished, while supplying a polishing agent to perform polishing by relative movement thereof, wherein the surface to be polished including a surface comprising silicon oxide of a semiconductor substrate is polished with the polishing agent according to claim 1 as the polishing agent.
 13. A liquid additive for polishing, which is a liquid additive for preparing a polishing agent by being added to a cerium oxide particle dispersion, the liquid additive comprising: a water-soluble polymer comprising a copolymer of a monomer (A) which comprises at least one member selected from the group consisting of an unsaturated dicarboxylic acid, a derivative thereof, and salts of the unsaturated dicarboxylic acid and the derivative thereof and a monomer (B) other than the monomer (A), comprising an ethylenic double bond and no acidic group; a pH regulator; and water, wherein: the liquid additive has a pH of 4 to 8.6; and at least a part of the unsaturated dicarboxylic acid is esterified. 